<template>
  <div class="alphabet">
      <ul class="list">
        <li
          class="item"
          v-for="item of letters"
          :key="item"
          :ref="item"
          @click="handleletterClick"
          @touchstart.prevent="handleTouchStart"
          @touchmove="handleTouchMove"
          @touchend="handleTouchEnd"
        >{{item}}</li>
      </ul>
  </div>
</template>

<script>
  export default {
    name:'Alphabet',
    props:{
      cities:Object
    },
    computed:{
      letters(){
        const letters = []
        for(let i in this.cities){
          letters.push(i)
        }
        return letters
      }
    },
    data(){
      return{
        touchStatus:false,
        startY:0,
        timer:null
      }
    },
    updated(){
      this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
      handleletterClick(e){
        this.$emit('change',e.target.innerText)
      },
      handleTouchStart(){
        this.touchStatus = true
      },
      handleTouchMove(e){
        if(this.touchStatus){
          if(this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() => {
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - this.startY)/20)
            if(index>=0 && index<this.letters.length){
              this.$emit("change",this.letters[index])
            }
          },16)
        }
      },
      handleTouchEnd(){
        this.touchStatus = false
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list{
    position:absolute;
    right:0;
    top:1.58rem;
    bottom:0;
    width:.44rem;
    display:flex;
    flex-direction:column;
    justify-content: center;
    .item{
      line-height:.4rem;
      text-align:center;
      color:$bgColor;
    }
  }
</style>
